This invention relates to a mechanism and method for extracting tubes from a tube sheet, and in particular, to a mechanism and method which compensates for variations, due to manufacturing tolerances, in the inside diameters of tubes being extracted from the sheet.
Heat exchange tubes are employed in heat exchange equipment of many types wherein the number of tubes used in any given unit may vary from one to literally hundreds. Typically, the tubes employed in heat exchangers are expanded into tube sheets or members.
At times, due to malfunctions or normal maintenance, it is necessary to replace one or even all of the tubes used in a given heat exchange unit. As may be readily recognized, the replacement of a tube requires that the heat exchange unit be removed from the particular cycle in which it is normally employed. Depending upon the installation, the removal of the heat exchanger from operation may result in either inefficient operation or total stoppage of the cycle. As is obvious, in such cases, the removal and replacement of the tubes must be accomplished as expeditiously as possible.
Even in installations wherein the temporary elimination of the heat exchanger from the cycle may not be critical, as for example where standby units are available, it is desirable that the tubes be removed as quickly as possible to minimize labor and related expenses.
Heretofore, various mechanisms have been employed for extracting tubes; however, such devices have not been entirely satisfactory for one or more reasons. In U.S. Pat. No. 3,369,287, there is disclosed a tube extracting mechanism which uses fluidic pressure to operate a first cylinder to expand a plurality of jaws into engagement with the inner surface of a tube. A second cylinder is thereafter actuated by fluid under pressure to extract the tube from its tube sheet. Extraction devices of this type are not entirely satisfactory since the jaws are expanded to a preset diameter, which does not take into account variations in the diameter of tubes due to such causes as manufacturing tolerances. In some cases, by expanding the jaws to a preset diameter, the tube and surrounding surface of the tube sheet may be damaged due to over expansion of the jaws; whereas in other cases, the jaws may be insufficiently expanded whereby the extraction of the tubes may become unduly difficult.